.ECIDIUM. 



[ 16 ] 



AERIAL ROOTS. 



polygonal. At a certain stage the apex of 

 the perithecium gives way, so that it forms a 

 kind of cup around the membrane enclosing 

 the mass of sporanges arising from the base. 

 The whole structm'e has by this time come 

 immediately up to the under side of the epi- 

 dermis, which is next ruptured, and the peri- 

 thecium with the sporanges are protruded, 

 more or less according to the habit of the 

 species (PI. 20. ^g.l,p,p). The upper 

 portions of the rows of cells composing the 

 peridial membrane then separate more or 

 less from each other, splitting into lobes, so 

 as to set the sporanges free, and form a kind 

 of cup with toothed margins seated in the ex- 

 panded perithecium (Woodcuts, figs. 5 & 6). 



The spores, which are at first deHcate cel- 

 lules, subsequently acquire a tough mem- 

 brane, increasing considerably in size, so as 

 to distend the parent utricle or sporange, 

 which is ultimately only recognizable where 

 it connects the spores together in a monili- 

 forai series. The spores in most cases now 

 acquire a deep yellow (except in ^. leucoco- 

 nium) colour, owing to contents chiefly ac- 

 cumulated in the centre. Their membrane 

 is colourless, then* form finally irregularly 

 polygonal, and the diameter varies much, 

 even in ripe spores of one and the same spe- 

 cies, from 1-1000 to 1-1800 of an inch. The 

 upper spores are often ripe at an epoch when 

 j^oung spores are still in course of produc- 

 tion at the lower end of the sporanges, 

 finally, however, the development ceases be- 

 low and the tube elongates a little beneath 

 the lowest spore, forming a kind of pedicle 

 or basidium to the row. The ripe spores 

 either soon fall apart and fill the cup as a 

 loose powder along with short incomj^lete 

 sporanges, or the rows persist even after they 

 mature, held together probably by a firmer 

 sporangial membrane. The cells of the pe- 

 ridial membrane undergo changes also, con- 

 temporaneously w'iih the ripening of the 

 spores, becoming thickened by internal de- 

 posits and acquiring a rough cuticle, giving 

 them a papillose or spiny aspect. This 

 cuticle, like that of the spore, is dissolved by 

 solution of potass; the cell-membrane which 

 it invests is coloured brown-yellow by sul- 

 phm'ic acid and iodine. Information regard- 

 ing the mode in which the jEcidia probably 

 become implanted in the vegetables they in- 

 fest, is contained under the head of Para- 

 sitic Fungi. 



The British species of jEcidium are nume- 

 rous; more than thirty are described by 

 Berkeley in the British Flora, many of which 



are common, especially those of the Mints, 

 the Compositse, such as the Coltsfoot, &c., the 

 BerberiTjtheGooseberry, Buckthorn, Spurge, 

 Nettle, &c. {^. Compositarum, Menthce, Ber- 

 beridis, Grossularice, crassum, Euphorbice, 

 Ui'ticce, §-c.). 



The species occurring upon Pomacese are 

 separated by Fries, and form the genus 

 Roestelia, Rebentisch ; among these are ^c. 

 [R.) cornutum, on the Mountain ash, and 

 cancellatum occasionally occumng in great 

 abundance on Pear-leaves. See Roestelia. 



BiBL. For Species : — British Flora, ii. pt. 

 2. p. 369 : Greville, Sc. Crypt. Flora, pis. 7j 

 Q2, 97, 180, 209. 



For Anatomy and Physiology : — Unger, 

 Die Exantheme, pp. 297, 300, t.3. f. 18, 19, 

 t. 4. ; Meyen, Pjianzenpathologie, pp. 143, 

 148-50; Tulasne, Comptes Rendus, March 

 24 and 31, 1851 ; Atin. des Sc. nat., ser. 3. 

 t. XV.; ibid, sew 3. t. vii. p. 45; Leveille, 

 Rech. sur le dev. des Uredinees ; Ann. des 

 Sc. nat. ser. 2. t. xi, ; Corda, Icones Fun- 

 gorum, iii, t. 3. f. 45 ; Anton, de Bary, Die 

 Brandpilze,'Bev\m, 1853, p. 55 et seq. pi. 5, 

 6 and 7- 



^GERITA, Persoon.— A genus of Mu- 

 corini (Physomycetous Fungi). ^. Candida, 

 Persoon, occurs upon damp decaying wood, 

 forming a white mealy coat. 



BiBL. Greville, Sc. Crypt, Flora, pi. 268. 

 fig.l. 



^NGSTRCEMIA, Br. and Sch.— A ge- 

 nus of Leptotrichaceous Mosses, including 

 certain Dicrana and Weissia, &c. of authors. 



1. jEngstrcemia cerviculata, C. Miill.:= 

 Dicr. cerviculatum, Hedw. 



2. ^. heteromalla, C. Miill. =Dicr. hete- 

 romallum, Hedw. 



3. ^. subulata, C. M\i\\.=Dicr. subula- 

 tum, Hedw, 



4. ^.curvata, C. Miill. =D^cr. ciirvatum, 

 Hedw. 



5. ^. varia, C. Miill. = Dicr. varium, 

 Hedw. 



6. JE. rufescens, C. M.u[\.= Dicr. rufes- 

 cens. Turn. 



7. ^.squarrosa, C. Miill. =Z)icr. squar- 

 rosum, Schrad. 



8. JE. Grevilliana,C. Miill.=Dicr. Schre- 

 berianum. Hook. 



9. yE. crisp a, C. Miill.^ Dicr. crispum, 

 Hedw. 



10. JS. cylindrica, C. Miill. =Dic?3/moc?ow 

 cylindricum. Hook. 



AERIAL ROOTS.— A very large pro- 

 portion of the exotic Orchids are epiphytic 

 plants and produce aerial roots, which ab- 



